1. Field of the Invention
This specification relates to an organic light emitting diode (OLED) device, and particularly, to an OLED device capable of preventing permeation of external moisture, oxygen and the like, and a fabricating method thereof.
2. Background of the Invention
Although cathode ray tube (CRT) display devices were widely used as a display device, flat panel display (FPD) devices, such as a plasma display panel (PDP) device, a liquid crystal display (LCD) device, an organic light emitting diode (OLED) device, which may be referred to as an organic electroluminescent display (OELD) device, and the like, have been the subject of recent research and development as substitutes of the CRT.
Among others, OLED devices as a self-light emitting device have advantages of a light weight and a thin profile due to omission of a backlight unit, which is used for the LCD devices as a non-light emitting device.
The OLED devices have a viewing angle and a contrast ratio superior to LCD devices, and have advantages in a power consumption so as to be driven with a direct current (DC) low voltage. Further, the OLED devices have a fast response speed, an excellent durability against an external impact by virtue of a solid internal display device and a wide operation temperature range.
Especially, the fabricating process of the OLED device is simplified, accordingly, the OLED device is less expensive to produce than the conventional LCD device.
The OLED devices exhibiting such characteristics may be classified into a passive matrix type and an active matrix type. In the passive matrix type OLED device, signal lines cross each other in a matrix pattern. In the active matrix type OLED device, a Thin Film Transistor (TFT) as a switching element is arranged for each pixel to switch on or off the corresponding pixel.
Since the passive matrix type OLED devices have disadvantages in resolution, power consumption, lifespan and the like, active matrix type OLED devices having advantages of high resolution and large screen have been the subject of recent research and development.
In terms of those characteristics, a structure of an OLED according to the related art will be described hereinafter with reference to FIGS. 1 and 2.
FIG. 1 is a sectional view schematically showing an OLED according to the related art.
FIG. 2 is an enlarged sectional view of a part “A” of FIG. 1, which shows a non-display area NA as panel edge portion of the related art OLED.
An OLED device 10 according to the related art, as shown in FIGS. 1 and 2, includes a first substrate 11 having a switching TFT (not shown), a driving TFT (not shown) and an organic light emitting diode (OLED) (not shown), and a second substrate 41 facing and encapsulating the first substrate 11. The first and second substrates 11 and 41 are spaced apart from each other, and attached to each other with a seal pattern 47 at an edge portion of the first and second substrates 11 and 41.
Here, a gate line (not shown) and a data line (not shown) which intersect with each other on a boundary of each pixel region (not shown) are formed on a display area AA of the first substrate 11, and a power line (not shown) may be formed in series with the gate line or the data line.
Each pixel region is provided with the switching TFT and the driving TFT.
A semiconductor layer 13 is formed on each pixel region within the display area AA of the first substrate 11, in correspondence with a driving region (not shown) and a switching region (not shown). The semiconductor layer 13 is made of silicon. The semiconductor layer 13 includes an active region 13a disposed at a central portion thereof for forming a channel region, and a source region 13b and a drain region 13c formed at both sides of the active region 13A with high levels of impurities doped thereon.
A gate insulating layer 15 is formed on the first substrate 11 including the semiconductor layer 13.
A gate electrode 17 facing the active region 13a of the semiconductor layer 13 and the gate line (not shown) connected to the gate electrode 17 are formed on each pixel region within the display area AA.
Also, a first interlayer insulating layer 19 is formed on the gate insulating layer 15 having the gate electrode 17 and the gate line. Here, the interlayer insulating layer 19 and its lower gate insulating layer 15 include first and second semiconductor contact holes (not shown), respectively, to expose the source region 13b and the drain region 13c located at both sides of the active region 13a. 
A source electrode 21 and a drain electrode 23 are formed on the first interlayer insulating layer 19 having the first and second semiconductor contact holes within each pixel region P. The source electrode 21 and the drain electrode 23 are spaced apart from each other and contact the source region 13b and the drain region 13c which are exposed through the first and second semiconductor contact holes.
In addition, a second interlayer insulating layer 25 is formed on the first interlayer insulating layer 19, which is exposed between the source electrode 21 and the drain electrode 23, within each pixel region P. The second interlayer insulating layer 25 includes a drain contact hole (not shown) for exposing the drain electrode 23 therethrough.
Here, the source electrode 21 and the drain electrode 23, the semiconductor layer 13 having the source region 13b and the drain region 13c, which contact those electrodes 21 and 23, and the gate insulating layer 15 and the gate electrode 17 both formed on the semiconductor layer 13 constitute the driving TFT (not shown).
Although not shown, the switching TFT (not shown) has the same structure as the driving TFT, and is connected to the driving TFT.
A first electrode 27, an organic light emitting layer 31 and a second electrode 33 are sequentially formed on an area where an image is actually displayed at the second interlayer insulating layer 25.
Here, the first and second electrodes 27 and 31 and the organic light emitting layer 31 interposed between the electrodes 27 and 31 constitute an organic light emitting diode (OLED) (or will be referred to as an organic electroluminescent (EL) diode) (not shown).
The first electrode 27 is electrically connected to the drain electrode 23 of the driving TFT. Here, the first electrode 27 serves as an anode, and the second electrode 33 serves as a cathode.
Accordingly, light from the organic light emitting layer 31 is emitted through the first electrode 27 according to a bottom emission method.
The organic light emitting layer 31 may have a single layer made of a light emitting material, or have multiple layers including a hole injection layer, a hole transport layer, an emitting material layer, an electron transport layer and an electron injection layer for improving emission efficiency.
Referring to FIGS. 1 and 2, the first electrode 27 is formed in each pixel region P, and a bank 29 is located between the adjacent first electrodes 27 formed in each pixel region P. Here, the bank 29 has a matrix shape of a lattice structure, and corresponds to a border between the adjacent pixel regions P such that the first electrode 27 is separated for each pixel region P.
A passivation layer 35 made of silicon nitride (SiNx) for preventing permeation of moisture is formed on the second electrode 33 which is formed on an entire surface of the organic light emitting layer 31 having the bank 29.
In addition, the first and second substrates 11 and 41 are attached to each other with a seal pattern 47 at the edge portion thereof. Accordingly, the OLED device 10 is encapsulated.
The seal pattern 47 seals the display area AA to prevent oxygen or moisture from being permeated into the display region AA. The seal pattern 47 is formed on the non-display area NA surrounding an edge portion of the display area AA.
In the related art OLED device 10 having the configuration, the first and second substrates 11 and 41 are attached to each other more strongly with the seal pattern 47.
Consequently, contaminants such as external moisture or gas from may be prevented from being permeated into a spaced gap between the first and second substrates 11 and 41.
In the meantime, to attach the first substrate 11 and the second substrate 41 to each other, an adhesive layer 45 is interposed between the first substrate 11, which includes the non-display area NA as the panel edge portion and the display area AA having each pixel region (not shown), and the second substrate 41.
Therefore, in the OLED device 10 according to the related art, when a predetermined voltage is applied to the first electrode 27 and the second electrode 33 in response to a selected color signal, holes injected from the first electrode 27 and electrons applied from the second electrode 33 are transported to the organic light emitting layer 31 and accordingly excitons are generated by the hole and the electrons. Light is generated by transition from an excited state into a ground state of the excitons. The light is then emitted in form of visible rays. Here, since the emitted light is emitted outwardly through the transparent first electrode 27, so that the OLED device 10 can display an image.
However, the related art OLED having the aforementioned configuration has the following shortcomings.
According to the related art OLED device, a single passivation layer is used to protect the OLED device from moisture. As shown in FIG. 2, when a foreign material 51 which is several μm large is present, it acts as a defect. Accordingly, moisture is permeated into the corresponding portion, which makes it difficult to ensure a lifespan of the device sufficiently.
Also, the passivation layer is usually made of silicon nitride (SiNx). The silicon nitride is deposited at low speed. Hence, in order to reduce the affection by a foreign material more than several μm in size, the silicon nitride has to be deposited thicker than several μm. However, this disadvantageously increases the deposition time, causing an increase in fabricating costs accordingly.